The present invention relates to peripheral buses for computer systems, and more particularly to a peripheral bus apparatus for connecting a computer system to multiple peripheral units that may all be mounted within the same enclosure.
The Small Computer System Interface (SCSI) standard (ANSI X3.131-1986) and the follow-on Small Computer System Interface II (SCSI-2) proposed standard, ANSI X3.131-199X, revision 10h, define high speed peripheral buses for use in small computer systems. Both of these standards are hereby incorporated by reference. These standards set forth the attributes of SCSI and SCSI-2 high speed peripheral bus systems. One such attribute is the distance between branches branching off from a SCSI-2 bus or a SCSI bus. According to paragraph 4.2.1 of the SCSI-2 proposed standard referenced above, for single ended SCSI-2 bus or a SCSI bus the spacing between branches is recommended to be at least 0.3 meters. The reason behind this recommendation is that systems with closer branch spacings tend to have signal integrity problems, especially for signals having the faster rise times set forth in the SCSI-2 standard. These signal integrity problems stem primarily from reflections at the connection points where branches branch off from the main bus.
Once the signal integrity problem was recognized, one proposed solution was to physically increase the distance between branch connection points while also keeping the branch length physically short. Thus, the SCSI-2 standard has a 0.1 meter maximum branch length as well as the 0.3 meter minimum spacing between branch connection points.
One known way to implement the 0.3 meter branch spacing recommendation is to use a flexible cable that is 0.3 meters long for the SCSI or SCSI-2 bus, and coil the cable up in such a manner that its two ends may be attached to the 0.1 meter branches at the branch connection points. This allows two branch connectors to be located physically near one another, yet electrically separated by the recommended 0.3 meters of wire. The problem of this approach is that these coils of cable are bulky and their installation requires substantial manufacturing costs.